1. Field of the Invention
The present invention relates to an element mapping apparatus and an element mapping image display method.
2. Description of the Related Art
An element mapping apparatus is an apparatus in which, for example, when an electron beam or an X-ray is irradiated on a small area of a sample by an electron beam source or an X-ray source, an characteristic X-ray such as a characteristic X-ray or a fluorescent X-ray emitted from the sample is detected by an X-ray detector, an analyzer such as a multi-channel analyzer measures the energy intensity or counts the energy from the output of the X-ray detector to produce an energy spectrum, an element mapping image is obtained corresponding to a pixel position according to the kinds of elements or analysis lines, and the element mapping image is stored in an element mapping memory provided for each element as element mapping data, in order to display a distribution screen comprised of the element mapping images of a set element on an image display device such as a CRT as needed.
For example, when a sample containing arsenic (As) and lead (Pb) is irradiated with an electron beam, and the characteristic X-ray or the scattered X-ray emitted from the sample is detected by an X-ray detector, an example of an energy spectrum at an arbitrary point in the sample obtained by an analyzer is shown in FIG. 5. Here, the horizontal axis represents energy, and the vertical axis represents the intensities or counts of the detected characteristic X-ray and the like. On the basis of this, the concentration of particular elements can be measured.
In addition, in most cases, each element has plural analysis lines acting as peaks indicating characteristic X-ray energies, such as a Kα line, a Kβ line, an Lα line, and an Lβ line.
Therefore, the energy positions of the Kα line 23 of As and the Lα line 20 of Pb overlap with each other, and there is a problem in that Pb may be identified as As.
Therefore, when a peak exists in the energy position of the Lα line of Pb but peaks of the Lβ line 21 and Lγ line 22 in other energy positions of Pb do not exist, it is determined that Pb is not contained in the sample.
Similarly, when a peak of As does not exist in a position of Kβ line 24 although the peak of the Kα line 23 does exist, it is determined that As is not contained in the sample.
As described above, the peaks (analysis lines) of plural characteristic X-rays are compared for accurate qualitative analysis.
In addition, when two X-rays are incident on the X-ray detector at a short interval, in some cases, the two X-rays are not distinguished from each other but measured as a single X-ray. In this case, a phenomenon called sum peak occurs in which a peak having the energy of the sum of the two X-rays is observed in the energy spectrum.
Accordingly, there is a problem in that, for example, Au is identified as Cd, since the sum peak generated as the Lβ line of gold (Au) overlaps with the energy position of the Kα line of cadmium (Cd).
However, in the case of an element mapping image of a sample which is two-dimensionally measured, qualitative analysis using an energy spectrum at an arbitrary measurement position as described above cannot be performed. Therefore, distribution screens that are plural element mapping images are displayed to compare the effects of overlapping elements, such as the overlapping of the energy peaks, in order to perform element identification or quantitative analysis.
FIG. 6 shows a method of displaying element mapping images in an existing element mapping apparatus.
Using a mouse or a keyboard, an operator sets the size or the number of distribution screens 17 such as element mapping images to be displayed in a parent window 11 on a display that is an image display device of the element mapping apparatus, and sorts the distribution screens 17 to be arranged and displayed. In an example of the existing technique, the twelve distribution screens 17 are displayed in the parent window 11.
Accordingly, in the case where the existence of a target element in a sample is determined using the element distribution image, an element mapping image of plural energy bands is displayed, and this causes the effects of the overlapping elements to be considered. Therefore, accurate determination can be made (for example, refer to JP-A-9-72868).
In addition, as another existing technique, an element analysis image display method is known which overlaps distribution screens that are plural element mapping images obtained by element analysis over one another so as to display them on the same screen at the same time and thereby enable easy recognition of the relationship between 2D information (for example, refer to JP-A-8-320298).
However, the existing element mapping apparatus has the following problems.
In the case where plural distribution screens such as the element mapping images are displayed on the parent window at the same time to determine the existence of a target element, the number of distribution screens that can be displayed on the parent window is limited. In addition, when a number of distribution screens are displayed, the display size for each distribution screen is reduced. Therefore, there is a problem in that it is difficult to determine whether or not the same element is distributed at the same regions of the distribution screens. Moreover, when alternately observing an element displayed at other positions, there is a problem in that it is difficult to determine the distribution state of the same distribution screen.
In addition, in the case where the distribution screens are displayed at the same time on the same screen in order to determine existence of a target element and overlap one another, an intensity contrast obtained by changing color or brightness depending on the detection intensity of the data of each particular element is set to be displayed. However, in regard to a portion where plural image data overlap, when the degrees of overlap or the intensity contrasts obtained by changing brightness corresponding to the detection intensity are different depending on each pixel of the display screen, in order to display the original elements and the analysis lines of different energies of each element during the overlapping operation as different display colors, the combination of colors or the intensity contrast combination of the colors becomes complex, and there is a problem in that it is difficult to determine the distribution state of the distribution screen.
In consideration of the above-mentioned problems, an object of the invention is to provide an element mapping apparatus capable of significantly improving the visual quality for determining the difference between element distribution states of element mapping images, without limiting the number or reducing the size of distribution screens such as the element mapping images, thereby enabling correct recognition of the element distribution states.